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Dissimilar joining of aluminium to ultra-high strength steels by friction stir welding
KTH, School of Industrial Engineering and Management (ITM), Production Engineering, Welding Technology.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Multi-material structures are increasingly used in vehicle bodies to reduce weight of cars. The use of these lightweight structures is driven by requirements to improve fuel economy and reduce CO2 emissions. The automotive industry has replaced conventional steel components by lighter metals such as aluminium alloy. This is done together with cutting weight of structures using more advanced strength steels. However, sound joining is still difficult to achieve due to differences in chemical and thermal properties.

 

This research aims to develop a new innovative welding technique for joining aluminium alloy to ultra-high strength steels. The technique is based on friction stir welding process while the non-consumable tool is made of an ordinary tool steel. Welding was done by penetrating the rotating tool from the aluminium side without penetrating into the steel surface. One grade of Al-Mg aluminium alloy was welded to ultra-high strength steels under lap joint configuration. Different types of steel surface coatings including uncoated, hot-dipped galvanised and electrogalvanised coating have been studied in order to investigate the influence of zinc on the joint properties. The correlation among welding parameters, microstructures, intermetallic formation and mechanical properties are demonstrated in this thesis.  Results have shown that friction stir welding can deliver fully strong joints between aluminium alloy and ultra-high strength steels. Two intermetallic phases, Al5Fe2 and Al13Fe4, were formed at the interface of Al to Fe regardless of surface coating conditions. The presence of zinc can improve joint strength especially at low heat input welding due to an increased atomic bonding at Al-Fe interface. The formation of intermetallic phases as well as their characteristics has been demonstrated in this thesis. The proposed welding mechanisms are given based on metallography investigations and related literature.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2017. , 39 p.
Series
TRITA-IIP, ISSN 1650-1888
Keyword [en]
Aluminium alloy, high strength steel, intermetallic, friction stir welding, dissimilar joining
National Category
Manufacturing, Surface and Joining Technology
Research subject
SRA - Production
Identifiers
URN: urn:nbn:se:kth:diva-207356ISBN: 978-91-7729-390-3 (print)OAI: oai:DiVA.org:kth-207356DiVA: diva2:1096788
Public defence
2017-06-09, M311, Brinellvägen 68, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
XPRES - Initiative for excellence in production research
Note

QC 20170519

Available from: 2017-05-19 Created: 2017-05-19 Last updated: 2017-05-19Bibliographically approved
List of papers
1. A study of weld formation in friction stir welding of electrogalvanised steel to aluminium alloy in lap joint configuration
Open this publication in new window or tab >>A study of weld formation in friction stir welding of electrogalvanised steel to aluminium alloy in lap joint configuration
(English)In: Journal of Materials Processing Technology, ISSN 0924-0136, E-ISSN 1873-4774Article in journal (Refereed) Submitted
Place, publisher, year, edition, pages
Elsevier
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:kth:diva-207187 (URN)
Note

QC 20170602

Available from: 2017-05-18 Created: 2017-05-18 Last updated: 2017-06-02Bibliographically approved
2. Intermetallic compounds in friction stirred lap joints between AA5754/galvanised ultra-high strength steel
Open this publication in new window or tab >>Intermetallic compounds in friction stirred lap joints between AA5754/galvanised ultra-high strength steel
2016 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, Vol. 21, no 8, 653-659 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents results of joining of AA5754 and DP800 based on the friction stir welding process. Joints were produced by the tool made of H13 tool steel which was allowed to penetrate through the aluminium sheet until reaching the surface of steel sheet without penetrating into it. This approach is an economic and robust way to operate the dissimilar welding process without excessive tool cost. Bonding was achieved by interfacial diffusion reactions between aluminium and iron with a formation of intermetallic compounds. The formation of brittle intermetallic compounds at the interface between the materials was studied. Three intermetallic phases were found at the interface including Al13Fe4, Al5Fe2 and Fe3Zn10. A range of process parameters was identified with a thickness of the intermetallic layers around 2 mu m. Shear fracture failure mode was observed under overlap loading. The mechanisms of formation of the joints and factors controlling the strength were discussed.

Place, publisher, year, edition, pages
Taylor & Francis, 2016
Keyword
Friction stir welding, Aluminium, Steel, Intermetallics, Diffusion
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-193276 (URN)10.1080/13621718.2016.1163878 (DOI)000382208600007 ()2-s2.0-84978488343 (Scopus ID)
Note

QC 20161007

Available from: 2016-10-07 Created: 2016-09-30 Last updated: 2017-05-19Bibliographically approved
3. Influence of zinc on intermetallic compounds formed in friction stir welding of AA5754 aluminium alloy to galvanised ultra-high strength steel
Open this publication in new window or tab >>Influence of zinc on intermetallic compounds formed in friction stir welding of AA5754 aluminium alloy to galvanised ultra-high strength steel
2017 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936Article in journal (Refereed) Published
Abstract [en]

In this study, lap joints between AA5754 and DP1000 ultra-high strength steels were producedby friction stir welding. In order to investigate the roles of zinc on intermetallic phase formation and joint properties, steel substrates were used, two being galvanised coated and one uncoated. Joint performance has been evaluated in term of maximum tensile shear loading. The effects ofthe process parameter, translational speed; chemical compositions; and intermetallic phase formationon the mechanical properties have been investigated. The results show that joints witha galvanised layer exhibit higher strength as compared to the non-coated steel. A thicker galvanisedlayer promotes the presence of zinc in the aluminium matrix, resulting in better jointproperties. The level of zinc contents in the aluminium matrix depends on process temperature and material circulation characteristics. Two stable Al-rich intermetallic phases, Al5Fe2 and Al13Fe4, were detected at the interface regardless of the coating conditions.

Place, publisher, year, edition, pages
Taylor & Francis, 2017
National Category
Manufacturing, Surface and Joining Technology
Research subject
SRA - Production
Identifiers
urn:nbn:se:kth:diva-207186 (URN)10.1080/13621718.2017.1302553 (DOI)
Funder
VINNOVA
Note

QC 20170519

Available from: 2017-05-18 Created: 2017-05-18 Last updated: 2017-05-19Bibliographically approved
4. A study of friction stir welded joint between AA5754 and ultra-high strength steel in hot dip galvanized condition
Open this publication in new window or tab >>A study of friction stir welded joint between AA5754 and ultra-high strength steel in hot dip galvanized condition
2014 (English)In: 10th Friction Stir Welding Symposium, Beijing, China, 2014, S2B-P5- p.Conference paper, Published paper (Refereed)
National Category
Other Engineering and Technologies
Research subject
SRA - Production
Identifiers
urn:nbn:se:kth:diva-161922 (URN)
Conference
10th Friction Stir Welding Symposioum, Beijing, China, 20‐22 May 2014
Note

QC 20150323

Available from: 2015-03-19 Created: 2015-03-19 Last updated: 2017-05-19Bibliographically approved

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